HTML Imports: A speculative fix for fast/dom/custom/imports-custom-element-abort.html

The test occasionally crashes by touching null HTMLImportsController:m_master in a timer function.
This change cancel the timer when m_master is cleared, and add an ASSERT() to make sure that
|m_master| is available when timer is fired.

BUG=355640
TEST=imports-custom-element-abort.html
R=dominicc

Review URL: https://codereview.chromium.org/209333012

git-svn-id: svn://svn.chromium.org/blink/trunk@169962 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/html/imports/HTMLImportsController.cpp

@@ -66,6 +66,7 @@ void HTMLImportsController::clear()
     if (m_master)
         m_master->setImport(0);
     m_master = 0;
+    m_recalcTimer.stop();
 }
 
 HTMLImportChild* HTMLImportsController::createChild(const KURL& url, HTMLImport* parent, HTMLImportChildClient* client)
@@ -166,13 +167,15 @@ void HTMLImportsController::stateDidChange()
 
 void HTMLImportsController::scheduleRecalcState()
 {
-    if (m_recalcTimer.isActive())
+    if (m_recalcTimer.isActive() || !m_master)
         return;
     m_recalcTimer.startOneShot(0, FROM_HERE);
 }
 
 void HTMLImportsController::recalcTimerFired(Timer<HTMLImportsController>*)
 {
+    ASSERT(m_master);
+
     do {
         m_recalcTimer.stop();
         HTMLImport::recalcTreeState(this);